Method of manufacturing cathodes for electron tubes



p 1967 SHUNZO OYABU ETAL 3,341,917

METHOD OF MANUFACTURING CATHODES FOR ELECTRON TUBES Filed April 22, 1964 2 Sheets-Sheet l an! I. m 7am: I Kl!) hreofl'brs /5407: a Qyz a 072. 0 M45 4 4 ATTORNEYS Se t. 19, 1967 SHUNZO OYABU ETAL 3,

METHOD OF MANUFACTURING CATHODES FOR ELECTRON TUBES 2 Sheets-Sheet 2 Filed April 22, 1964 ATTORNEYS United States Patent Y O 3,341,917 METHOD OF MANUFACTURING CATHODES FOR ELECTRON TUBES Shunzo Oyabu and 5111120 Masuda, Kyoto, and Hiroyukl Matsumoto, Takatsuki-shi, Japan, assignors to Matsushita Electronics Corporation, Osaka, Japan, a corporation of Japan Filed Apr. 22, 1964, Ser. No. 361,799 Claims priority, application Japan, Apr. 30, 1963, 38/ 22,968 6 Claims. (Cl. 29-2514) The present invention relates to a method of manufacturing a cathode for electron tubes, and more particularly to an improved method of making a small-sized flat cathode which operates highly effectively when incorporated in electron tubes such as miniwatt cathode ray tubes.

In conventional methods of manufacturing cathode heater elements of flat coiled shape adapted for incorporation in electron tubes of the type described above, complicated processes and specially designed take-up means have generally been required, and there has been a demand for a simplified method of making the same.

The primary object of the invention is to provide an improved and simplified method of manufacturing a miniature cathode especially suitable for incorporation in miniwatt electron tubes such as miniwatt cathode ray tubes.

Other objects and particularities of the invention will become obvious from the following description with reference to the accompanying drawings, in which:

FIG. 1 is a schematic side elevational view showing the step of shaping a composite article in a manufacturing method of the invention;

- FIG. 2 is a sectional side elevational view of the composite article deformed by the step shown in FIG. 1;

FIG. 3 is a perspective view of a finished cathode heater element obtained from vthe composite article of FIG. 2; 7 FIG. 4 is a perspective view of a directly heated cathode incorporating therein the cathode heater element as shown in FIG. 3', with a part broken away to show the cathode heater element disposed therein;

FIG. 5 is a schematic side elevational view showing the step of forming a composite structure for the purpose of obtaining a cathode heater element with an insulating covering thereon by the method according to the invention;

FIG. 6 is a perspective view of the composite structure made by the step of FIG. 5;

FIG. 7 is a perspective view heater element obtained shown in FIG. 6;

FIG. 8 is a perspective view of another form of the directly heated cathode which is formed from the insulated cathode heater element obtained by the step shown in FIG. 5; and

FIG. 9 is a modification of the forming step shown in FIG. 5.

The invention will now be described in detail with reference to the drawings. Referring to FIG. 1 at first, there is shown a basic concept of forming a cathode heater element according to the invention. In FIG. 1, it will be seen that a composite article 1 is interposed between a pair of dies 4 and 5 which are disposed on opposite sides of the composite article 1. The composite article 1 con sists of a mandrel 2 of a soluble wire of a metal, such as molybdenum, about which a heating filament 3 of tungsten is wound with a suitable pitch between every two adjacent turns. When now the dies 4 and 5 are moved towards each other to apply a suitable pressure to the composite article 1 to crush the same flatwise, the comof a finished cathode from the composite structure 3,341,917 Patented Sept. 19, 1967 posite article 1 is deformed as shown in FIG. 2, so that the mandrel 2 and the heating filament 3 take the form of flat portions 6 and -7, respectively.

Then, the composite article 1 having been deformed as shown in FIG. 2 is soaked in a solution such as of a mixture of nitric acid and sulfuric acid for removing the mandrel 2 alone by the selective dissolution. Subsequent- 1y, unnecessary portions at opposite end edges of the flat heating filament 7 are cut off and the ends are bent to form conductive terminals 8 thereat to obtain a cathode heater element in the form of a flat coil as shown in FIG. 3.

The cathode heater element, as shown in FIG. 3, obtained by the manufacturing method according to the invention is subsequently subjected to processes, as will be explained hereinunder, to provide a directly heated cathode.

Or, more precisely, a directly heated cathode as shown in FIG. 4 can be formed by providing an electron emissive oxide layer on the entire surface, except the conductive terminals 8, of the cathode heater element shown in FIG. 3 by well-known means such as spray coating, electro-deposition or immersion. In FIG. 4, it will be seen that the directly heated cathode includes a cathode heater ele'ment 9 embedded in an electron emissive oxide layer 10.

By the application of the manufacturing method of the invention, it is also possible to obtain a flat cathode heater element having thereon an insulating covering. One of such manufacturing processes is illustrated in FIG. 5. In FIG. 5, it will be seen that a frame member or a mold 11 of high-temperature resisting material preferably of molybdenum is placed on a fiat plate 12, and a deformed composite article 14 as shown in FIG. 2 is disposed within an aperture 13 of the mold :11. In a space 15 between the aperture 13 and the deformed composite article 14, an insulating material 16 in the form of paste is filled by use of a pallet 17. The insulating material 16 may comprise aluminum oxide kneaded with distilled water or a solution of nitrocellulose. This filling operation should be made on opposite sides of the composite article 14 by at first applying the paste 16 as shown in 'FIG. 5 and then inverting the mold 11 upside down on the fiat plate 12 to apply the paste on the opposite side of the composite article .14, except a special case as will be described later.

After this filling operation, the flat plate 12 is removed, and a structure of the three elements, that is, the mold 11, the deformed composite article 14 disposed in the aperture 13 of the mold 11 and the insulating material 16 enclosing the composite article 14 therein, or a structure of the two elements, that is, the deformed composite article 14 enclosed in the insulating material 16, is heated in a hydrogen atmosphere at a high temperature of the order of 1600 to 1700 C. In the case of the structure of the three elements, the mold 11 is then removed by some suitable mechanical means. Subsequently, both end edges of the structure are shaped to form conductive terminals 18 thereat to obtain a composite structure as shown in FIG. 6.

Thereafter, the composite structure is subject to a conventional process of selective dissolution to selectively remove the flat mandrel :6 alone to obtain a cathode heater element covered with insulating material as shown in FIG. 7. A layer or layers of electron emissive oxide may be provided directly on one face or both faces of such cathode heater element to form a directly heated cathode or an indirectly heated cathode.

In one form of a directly heated cathode shown in FIG. 8, an insulating layer 19 is provide on one face of the fiat heating filament 18, while an electron emissive oxide layer 20 is provided on the other face of the filament 18.

The directly heated cathode with such structure is sturdy and has an excellent thermal efficiency. Therefore, it is quite effective for use in miniwatt cathode ray tubes. It will be understood that the insulating layer 19 can be provided by applying the pallet 17 solely to one face of the composite article 14 in the process shown in FIG. 5, instead of filling the insulating material 16 from both sides of the article 14.

Although in the above embodiment the process as shown in FIG. has been used to obtain the composite structure as shown in FIG. 6, it will readily be understood that such composite structure can likewise be obtained by a process as shown in FIG. 9. In FIG. 9, there is shown a pair of dies 27 and 28 which form a press means. In a recess 29 in one of the dies 28, a predetermined amount of an insulating material 30, preferably powdery aluminum oxide, is filled and a deformed composite article 31 as shown in FIG. 2 is embedded in the insulating material 30. When now the die 27 is urged toward the die 28 to apply a pressure of the order of to kg/rnm. to the insulating material 30 enclosing therein the composite article 31, the composite article 31 is firmly bonded to the insulating material 30 to form a unitary structure, and a composite structure as shown in FIG. 6 can be taken out of the recess 29 in the die 28.

In any case, the external dimensions of the cathode heater element 21 covered with insulating material can easily be regulated in the process shown in FIG. 5 or 9. Therefore, by suitably selecting the shape of the aperture 13 of the mold 11 or the recess 29 of the die 28, the cathode heater element covered with insulating material which has a flat and smooth surface and any desired external shape can be obtained regardless of the shape of the heating filament.

What is claimed is:

1. A method of manufacturing a cathode element for electron tubes comprising the steps of coiling a heating filament about a unitary mandrel of soluble metal, applying pressure to deform said assembled heating filament and mandrel together into close fitting unitary relation, providing a coating layer of material on at least one surface of said assembled and flattened filament and mandrel and selectively removing said flattened mandrel by selec tive dissolution.

2. A method of manufacturing a cathode element for electron tubes according to claim 1 in which said layer is a layer of electron emissive oxide.

'3. A method of manufacturing a cathode element for electron tubes comprising the steps of coiling a heating filament about a unitary mandrel of soluble metal, applying pressure to deform said assembled heating filament and mandrel together into close fitting unitary relation, providing a coating layer of insulating material on at least one surface of said assembled and flattened filament and said mandrel, sintering said insulating material at a suitable temperature, and selectively removing said flattened mandrel by selective dissolution.

4. A method of manufacturing a cathode element for electron tubes according to claim 3 in which a layer of electron emissive oxide is directly formed on one face of said layer of insulating material after said step of removal of said flattened mandrel.

5. A method of manufacturing a cathode element for electron tubes according to claim 3 in which a layer of electron emissive oxide is directly formed on each face of said layer of insulating material after said step of removal of said flattened mandrel.

6. A method of manufacturing a cathode element for electron tubes comprising the steps of coiling a heating filament about a mandrel of soluble metal, applying pressure to flatten said heating filament and said mandrel in unitary relation, providing a coating layer of insulating material on one surface of said assembled and flattened filament and mandrel, sintering said insulating material at a suitable temperature, selectively removing said flattened mandrel by selective dissolution, and providing a layer of electron emissive oxide on the other surface of said heating filament after the selective removal of said flattened mandrel.

References Cited UNITED STATES PATENTS 1,767,716 6/1930 Stoekle 29-l55.68 X 2,287,460 6/ 1942 Wagenhals 29155.68 X 2,394,474 2/1946 Peters 313-344 2,482,826 9/1949 Bender 7 l.5 X 2,548,592 4/1951 De Michele 29155.68

WILLIAM I. BROOKS, Primary Examiner, 

1. A METHOD OF MANUFACTURING A CATHODE ELEMENT FOR ELECTRON TUBES COMPRISING THE STEPS OF COILING A HEATING FILAMENT ABOUT A UNITARY MANDREL OF SOLUBLE METAL, APPLYING PRESSURE TO DEFORM SAID ASSEMBLED HEATING FILAMENT AND MANDREL TOGETHER INTO CLOSE FITTING UNITARY RELATION, PROVIDING A COATING LAYER OF MATERIAL ON AT LEAST ONE SURFACE OF SAID ASSEMBLED AND FLATTENED FILAMENT AND MANDREL AND SELECTIVELY REMOVING SAID FLATTENED MANDREL BY SELECTIVE DISSOLUTION. 